n = int(input())
s = input().strip()

count = 0
remaining = []
for c in s:
    if c in {'3', '5', '7'}:
        count += 1
    else:
        remaining.append(c)

i = 0
max_i = len(remaining) - 1
additional = 0
while i < max_i:
    if remaining[i] == '1':
        next_char = remaining[i+1]
        if next_char in {'1', '9'}:
            additional += 1
            i += 2
        else:
            i += 1
    else:
        i += 1

print(count + additional)